Renewable Energy Winner: Northumbrian Water Group

As the first company to utilise thermal hydrolysis advanced anaerobic digestion (AAD) on an industrial scale, it is safe to say that Northumbrian Water Ltd (NWL) is a front runner for environmental and engineering excellence in the water industry.

L-r: Edie energy and sustainability editor Leigh Stringer, compere Sue Perkins and the Northumbrian Water team

Since 2006, Northumbrian Water strategically focused its AAD sludge treatment capacity at just two locations - one in Bran Sands in Teesside and one in Howdon in Tyneside. With a total investment of £75m, both plants currently use 100% sewage sludge to produce energy, which, according to Northumbrian Water, is an industry first.

The process equates to 1,000,000 tonnes of sewage sludge, from a population equivalent to three million people, into 9MW of green energy and employs AAD in a novel thermal hydrolysis process (THP), instead of sludge drying, to produce greater quantities of biogas than is possible using conventional anaerobic digestion.

As a result, Northumbrian Water expects emissions per megalitre, which is the normalised basis of comparison between water companies, will become the lowest in the country, while its ambition for emissions reduction of 35% by 2020, from a 2008 base, exceeds that of both the UK Government and the EU.

According to the company, latest figures show that emissions have fallen by 20% in the last four years, while today NWL is treating 300,000 tonnes of sludge cake per annum to produce around 80,000 MWh of renewable electricity, or 40% of the energy needs for the entire cycle of pumping and treatment of wastewater in the company.

However, making these sort of operational improvements has been on the company's agenda for over 15 years. Up to 1995 all of NWL's sewage sludge was transported by ship and disposed of at sea, when in 1997 it replaced this practice by investing in an award winning regional sludge treatment centre (RSTC) which dried raw sludge, making it relatively unique in Europe.

This maximised the potential for the sludge to be used as a fuel by maintaining a higher calorific value in the final product which provided a sustainable disposal outlet, either to agriculture or as a fuel.

Since then, concerns about the application of sludge to land have receded, energy costs have risen and climate change has become recognised as one of the greatest challenges to our future. In order to stay a head of the game and tackle these issues, the company has ensured that technological development has led its operations.

NWL's achievement is highlighted by claims that AAD plants are complex and costly, making them uneconomic to employ on sites where sludge volumes are low.

Its success is now seeing other water companies follow suit as NWL spreads the environmental benefits across the UK and further afield, expanding awareness in the industry by sharing commissioning experiences with fellow water companies so they can also reap the benefits.

NWL continues to push the barriers of producing energy from sewer waste and is currently investigating how to clean and directly inject biogas into the national gas grid and introducing alternative feedstock's (e.g. food waste) to increase site performance.

JUDGES' COMMENTS: This is innovation in a sector that needs to be pulled along by the nose a bit. If something like this has potential and encourages other Water Companies to go down this route that's great. They've done it at two sites - it's at scale, so they've not mucked about